Arc and spark extinguishing contacts utilizing single domain magnetic particles

ABSTRACT

This invention relates to contacts which have about 0.001 to 96 percent by weight of ferromagnetic or ferrimagnetic permanent magnetic particles embedded in the contacts such that the magnetic particles are distinguishable from the basic contact material. The Curie temperature of the magnetic particles used in the contacts are greater than about 250* C. and the magnetic particles have an average spontaneous magnetic energy product greater than about 5,000 Gauss.Oersted. The magnetic particles having spontaneous magnetic energy can also be incorporated in certain contact configurations to also obtain excellent noise suppression characteristics.

United States Patent [72] Inventor Peter A. Denes 9101 Crestwood Ave. N.E., Albuquerque, N. Mex. 87112 [2]] Appl. No. 877,261 [22] Filed Nov. 17, 1969 [45] Patented Dec. 7, 1971 [54] ARC AND SPARK EXTINGUISl-IING CONTACTS UTILIZING SINGLE DOMAIN MAGNETIC PARTICLES 23 Claims, 7 Drawing Figs.

[52] U.S.Cl 200/144 C, 200/147 A, 200/ l 66 C [51] Int.Cl ll0lh 9/30, I-lOlh 33/00 [50] Field of Search H01h/9/30; 200/144.2,166C,147,147 A, 147 B [56] References Cited UNITED STATES PATENTS 2,506,991 5/1950 Brown 200/166 X 2,854,074 9/1958 Frank et al 200/166 X 2,957,255 3/1961 Lafferty 200/144 3,008,022 11/1961 Lee 200/144 3,014,104 12/1961 Cobine et a1 .l 200/166 X 3,239,635 3/1966 Baude ZOO/166 3,281,563 10/1966 Waterton 200/166 3,379,846 4/1968 Wood et al. 200/144 3,485,978 l2/l969 Grind ell ZOO/144 OTHER REFERENCES Westinghouse Engineer, Aug. 1942, pp. 71- 74 General Electric Review, Apr. 1942, Vol. 45, pp. 21 1- 213 AIEE Transactions, 1940, Vol. 59, pp. 1017- 1024 Primary ExaminerD. F. Duggan Assistant Examiner-Mark O. Budd Attorney-Spensley and Horn ARC AND SPARK EXTINGUISI-IING CONTACTS UTILIZING SINGLE DOMAIN MAGNETIC PARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the field of electrical contacts and more particularly to electrical contacts with spark or arc extinguishing and noise suppression characteristics.

2. Description of the Prior Art It is known that the magnetic fields can be utilized for extinguishing electrical sparks or arcs which are generated during the breaking or making of contacts in electrical switching applications. The application of magnetic fields for this purpose has resulted in increasing the current handling capability of switches. In the past, to obtain a magnetic field, switches were built with permanent magnetic blocks around or underneath the contacts. In somecases electrical current was conducted through a coil surrounding the contacts so that the current to be connected or interrupted by the switch also supplied the needed magnetic field.

Since the additional magnetic structures described above made the resultant switches too bulky, other solutions to the arcing and sparking problem have been attempted. For example, magnetizable particles such as iron or nickel have been incorporated into switch contacts. In theory these magnetizable particles get magnetized by the through-flowing current and then should extinguish the are. However, in practice, the magnetizing loop of the through-flowing current is generally quite great, including the equipment through which the currentloop returns; thus, the magnetizing field and the magnetic energy product is extremely low. Therefore, the contacts magnetized by through-flowing current have relatively little arcextinguishing effect, if any.

SUMMARY OF THE INVENTION The present invention solves the shortcomings of the prior art techniques and allows the production of switches that have very strong magnetic blowout effects without increasing the overall size of the switch. Maintaining the overall dimensions of the switches having arc-extinguishing features is especially important in todays technology where miniaturization is often an important or critical factor.

The contacts made according to the teachings of the present invention have distinguishable magnetic particles embedded therein. However, contrary to the prior art, an adequate percentage of the distinguishablemagnetic particles of this invention are spontaneous permanent magnets and hence their magnetic energy is strictly independent from the current which flows through the switch contacts. Although it is possible to magnetize in electrical contacts magnetic particles which have no spontaneous magnetism, such contacts would be protected for only one operation because generally the are produced heats up the base areas on the contacts which results in their losing their magnetism. This latter effect occurs because the magnetized particles, having once gone through the Curie temperature, lose their permanent magnetism and cannot regain their magnetism, even'when cooled off, unless there is spontaneous magnetization. A remagnetization of contacts having no spontaneous magnetizable particles after each switching is impossiblefor all practical purposes. Thus the present invention teaches the required structure and method for obtaining electrical contacts having embedded therein distinguishable magnetic particles (e.g., ferromagnetic or ferrimagnetic) with spontaneous magnetic energy for effectively extinguishing arcs and blowing out sparks caused during the making and breaking of the contacts. Also, certain contact structures and switch configurations are disclosed for reducing unwanted noise effects caused during the operation of the switch contacts.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the general characteristics of intrinsic coercive force versus particle size for soft" and har magnetic materials;

FIG. 2 is a cross-sectional view illustrating one embodiment of the invention in which a shield member is used in conjunction with the invented electrical contacts;

FIG. 3 is a top plan view of a contact which exhibits lownoise effects;

FIG. 4 is a front elevational view showing a contact configuration for another embodiment of the present invention in which reduced noise effects can be achieved;

FIG. 4A is a top plan view of the contact shown in FIG. 4; and

FIGS. 5 and 5A are cross-sectional views showing differentoperating positions of one embodiment of a'switch structure utilizing the contact configuration shown in FIG; 4 and FIG. 4A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An adequate percentage of the magnetic particles used in the contacts of the present invention have a spontaneous permanent magnetism as will be described in detail below. It is known that in reducing the size of the magnetic particles, a critical size can be reached at which the particles consist of one single domain exhibiting a strong permanent magnetic energy. The single domain size is generally quite small. In the case of a cubic iron crystal, for example, the linear dimension is in the range of a couple of hundred Angstroms. However, the single domain size is quite different for various magnetic materials and by introducing additional anisotropic factors, like the strong dimensional asymmetry of a needle shape, the length of the crystal may be made much longer. It is a common characteristic for ferromagnetic and ferrimagnetic materials to have the coercivity and the magnetic energy product start to increase below a certain particle size until a maximum point is reached (see FIG. I).

In FIG. 1 a typical graphic plot of intrinsic coercive force (H versus particle size is shown. Curve C is characteristic of the so-called soft magnetic materials which are easily demagnetized if their particle size is large compared to the critical size and curve C of the hard" magnetic materials which are not easily demagnetized once magnetized. The hard magnetic materials have a large coercivity even in large particles because of the great crystal anisotropy, strain anisotropy, etc. In table I typical values of intrinsic coercive forces are listed by way of example, for various representative materials and particle sizes.

It is not necessary to achieve the maximum spontaneous magnetic energy product, which would involve percent of single domain particles, in order to obtain a feasible contact system. Feasible systems can be obtained with particles of various sizes having an average spontaneous magnetic energy product of at least about 5,000 Gauss.0ersted. However, it

should be understood that greater energies generally give better results. The present state of the art and the new techniques discussed herein allow the safe production of particle sizes and shapes of suitable magnetic materials which can exhibit average spontaneous magnetic energy products greater than 1,000,000 Gauss.0ersted.

As shown in table I, the optimum, or an adequate size distribution, of magnetic particles depends on the type of material selected. Also, factors such as the particle shape and precipitated impurities must be considered, therefore, it

average spontaneous magnetization with energy levels of at least about 5,000 Gauss.0ersted.

Whenever magnetic particles are heated higher than their Curie temperature, they lose their magnetism, Although this phenomenon occurs mainly on the surface of the contacts, this is where the magnetic particles which are the most effective for are extinguishment or blowout are located, since they are the closest to the base of the arc. Therefore, it is advisable to choose a magnetic material which has a high-Curie tempera- .ture. For low-current, low-voltage switches, a magnetic material having a Curie temperature of 250 C. has been found to be quite adequate. For larger currents or voltages correspondingly higher Curie temperatures are required. In this latter respect, cobalt and cobalt alloys are very useful as their Curie temperature are in the range of the melting point of silver.

Particles having a spontaneous magnetic energy regain their magnetism after being cooled below their Curie temperature. Therefore, such magnetic particles need no outside source of magnetization. The direction of the spontaneous magnetic field is of some importance since the direction of the arc movement is perpendicular both to the magnetic and electrical fields. If the magnetic particles are randomly mixed with the contact material particles, the spontaneous magnetic field vectors are also randomly oriented. This random configuration does not necessarily blow out the are immediately but keeps the base point of the arc moving on the surface of the contact in a steady but rapid manner. The movement of the base of the arc in this way impedes the heating effects of the are thus preventing the temperature from reaching a point at which it could supply ions. Hence, the arc will become extinguished in a relatively short interval of time.

While such a random structure may be satisfactory in many cases, it can be significantly improved. A specific orientation of the spontaneous magnetic vectors greatly increases the available energy.

A simple method of orienting magnetic particles having great crystal or dimensional asymmetry may be achieved by mechanical means known in the art. The individual vectors, however, still may form 180 angles, for example, and the strong unidirectional magnetic fields would then have only small dimensions. Although such partially oriented systems are more effective than a random system, they still keep moving the base point of the arc around before there is a complete blowout. The arc movements are, however, much faster in the stronger magnetic field.

A complete orientation in the desired direction can be obtained by magnetic means. The blowout or extinguishing effect of such oriented systems is clearly the most effective and the fastest.

Examples of some magnetic particles which are usable in switch contacts according to the present invention are listed in table II below.

4 Table 11 Maximum Magnetic Energy Product Curie Temperature Material in Guuss.0crsted C.

XIO'" Iron 3 770 Nickel l 358 Cobalt I I 1.130 Iron-Cobalt alloys 6 770 to 1130 Manganese-Bismuth 4 350 Cobalt Platinum 9 500 CuNiCo 2 I 950 Alnico v 5.5 Vicalloy 3.5 v 700 Cobult-Sumarium 20 850 Barium Hexaferrite 3.5 400 When selecting the appropriate magnetic material, in addition to the magnetic energy product, attention should be directed to other chemical, mechanical and electrical properties, such as oxidation, prevention of contact welding, mechanical strength, machinability, contact resistance, etc. Since these other properties of the materials are not per se the subject matter of this invention, and are generally well known in the art, no further elaboration is necessary except for drawing attention to the fact that they must also be considered when selecting a suitable material for a particular application.

The list of contact materials which can be mixed with the desired magnetic particles is very broad. Any of the known contact materials are suitable, such as, copper, the noble metals, their alloys, refractory compounds like carbides, nitrides, silicides, and their mixtures with noble metals or copper, etc. Further, specific additives can be provided for various known purposes, such as, for the prevention of welding when making the contacts with various metals or oxides. Also, easily subliming arc-cooling additives can be provided, such as, cadmium, indium, or their oxides, etc.

The ratio between the contact and magnetic materials can vary within fairly wide proportions, depending on the requirements and applications for the contacts. Some magnetic materials themselves can be used as contacts, for example, platinum-cobalt or cobalt-nickel-copper alloys in which case a binder material is needed to hold the particles together. One suitable binder system giving excellent results comprises a mixture of percent silver powder and 5 percent glass powder having a melting point of about 700 C. It has been found that 4 percent of this mixture can then be mixed with 96 percent magnetic contact powder and after compacting the mixed powders, a heat treatment at 700C. melts the glass and completes the bond. All percentages stated herein are weight percentages unless otherwise specified.

If the contacts have to interrupt high-voltage low-amperage currents (e.g., 200 to 5,000 volts, 0.] to 10 Amps), the contact resistance is of little interest and the weight percentage of the magnetic material may be as high as 80 percent, for example. For medium voltage large amperage applications (e.g., l 10 to 600 Volts, 10 to 250 Amps), magnetic particles in an amount of 3 to 50 percent are desirable, depending on the characteristics of the materials and currents. Finally, if a lowvoltage, low-amperage switch (e.g., 2 to 28 Volts, 0.01 to 0.1 Amps) of long life span and low-contact resistance is the goal, even a few tenths of a percent of the magnetic particles is satisfactory for keeping a' small spark moving. Also, the presence of the magnetic materials will decrease the possibility of obtaining roughened contact surfaces caused by spark erosion which after a while may result in appreciably increasing the contact resistance. Although certain ranges of voltages and currents are mentioned herein, these are for purpose of iilustration only. Depending on the application of the contacts it has been found that about 0.00l to 96 percent of permanent magnetic particles can be used in the contacts.

It should be mentioned that although in most cases one homogeneous magnetic metal, alloy or compound is satisfactory, in some cases it may be advantageous to employ two or more different kinds of magnetic particles. That may be advisable if the side effects of a particular magnetic system are undesireable, for economic or other reasons. As an example, cobalt-platinum particles have high-magnetic energy products, and low-contact resistance but are very expensive. These particles will move the base point of an are very fast. The high speed of the arc base would be little influenced if the magnetic particles are somewhat diluted with less expensive magnetic particles. Another example where a mixture may be desirable is where barium hexaferrite is used. Barium hexaferrite is quite inexpensive, but may noticably increase the contact resistance. The dilution of barium hexaferrite with cobalt particles, for example, would lower the contact resistance and not substantially diminish its magnetic effects for extinguishing arcs.

Among the numerous advantages of contacts having the described compositions and properties, a few will be briefly discussed. One major advantage is long service time which results because the consumption of the contacts by spark or are erosion during contact interruption or by material transfer during contact closure is greatly reduced by limiting the duration of sparks and arcs. The contacts can safely interrupt or connect much larger currents without the danger of a steady arc or the formation of a weld between the contacts. The contact surfaces using the invented structure remain substantially cleaner in the absence of prolonged arcing thus allowing a substantially constant contact resistance to be maintained.

Some examples for manufacturing the invented contacts will be discussed in detail. The production methods for obtaining spontaneously magnetized particles may be broadly classified as mechanical, chemical and electrochemical and combinations thereof. Some of the methods are generally known in the art for manufacturing such magnetic particles. Some methods will be described which not only produce the mag netic particles but simultaneously distribute the magnetic particles in the contact materials. The examples given will also discuss methods for making the invented contacts from mixtures of magnetic and contact particles, or from partial and complete subproducts of distributed particles by pressing, sintering, hot pressing, cold and hot welding etc. Partial orientation of the magnetic particles can be achieved by mechanical means and complete orientation by magnetic means. These methods will also be discussed in some of the various examples.

The possible combinations of producing various contact materials and contacts containing spontaneously magnetized magnetic particles are innumerable. In the examples, presented herein, a few typical systems will be described and a few typical production methods will be discussed. It should be understood that in addition to the systems and methods described in these specific examples, the invented product may be produced by many other methods which will be apparent to those skilled in the art in light of the present disclosure.

EXAMPLE 1 Iron oxide may be reduced in dry hydrogen at a temperature less than about 300 C. The end product of this chemical process is very fine metallic iron having an average particle size of approximately 200 Angstroms. The majority of these iron particles exhibit single magnetic domains. About percent of the fine iron particles are thoroughly mixed with about 90 percent silver oxide particles in a nitrogen atmosphere. Then the mixture is heated up to 300 C. in a hydrogen atmosphere, to reduce the silver oxide to metallic silver. The particles are then compressed into contacts at room temperature by the application of a pressure of about 10 tons per square inch. Annealing in a nitrogen atmosphere at 300 C. and compression may be repeated several times if needed and if higher densities are desired.

EXAMPLE 2 Another chemical method can be used to supply a fine distribution of the contact material and of the spontaneously magnetized magnetic material. This method is the decomposition of suitable chemical compounds comprising two ro more metals of interest. For example, silver ferro-cyanide, Ag Fe(CN) may be heated in vacuum to 400 C., generating in this way a mixture of fine silver and iron particles. The absence of oxygen in the compound and in the ambient environment results in the avoidance of oxidation to the iron. The iron content in the contact material is about 1 L5 percent. Using another compound, such as silver ferri-cyanide, Ag Fe(CN) for example, 15 percent iron may be obtainable in the mixture. The contacts can then be made by hot pressing at about 500 C. and 20,000 p.s.i.

EXAMPLE 3 If during a vacuum decomposition of a suitable chemical compound an outside orienting magnetic field is applied, the generated magnetic particles will grow in the direction of the magnetic field creating a longitudinal anisotropy. Thus, the highest magnetic energy product for the particles will be aligned in the direction of the outside applied magnetic field. Particles formed in this manner have high-remanence and high-intrinsic coercive force which result from the magnetic orientation and strong dimensional anisotropy. The particles can be compacted into contacts by hot pressing, with or without magnetic orientation, before pressing.

EXAMPLE 4 Mixtures of chemical solutions of magnetic and contact particles can be converted at high temperatures to a fine mixture of the oxides and metals of the original ingredients. The components may be chosen in a way that after cooling the particles, a low-temperature reduction may selectively reduce only the contact metals and maintaining the magnetic oxides or oxide compounds; or, the reduction would reduce both the contact metals and the magnetic metals or alloys. Solutions of barium acetate, ferrous acetate and silver acetate in dilute nitric acid may be mixed in a proportion having substantially the following atomic ratio, for example, Ba:Fe:Ag:=l :l2:l50. The mixture is then sprayed as a fine mist into a reaction tube operated by a gas flame. The mixture is converted in the reaction tube to a thorough solid-state mixture of fine barium hexaferrite particles and silver-silver oxide particles. These particles are then hot pressed into contacts. During the heat treatment, the silver oxide reduces to metallic silver. Magnetic orientation and/or mechanical partial refinement may be applied as discussed in detail in the following examples.

EXAMPLE 5 The most simple mechanical production method is mixing pulverized contact material and the chosen magnetic particles together and then sintering them to obtain the desired density. Since chemical reactions between the contact material and magnetic particles should be minimized, pressure sintering is considered to be the desired method which allows high densities to be obtained at lower temperatures. In this example, the contact material is about percent by weight pure silver and about 10 percent by weight barium hexaferrite powder. The barium hexaferrite powder is composed of hexagonal platelets exhibiting an average length to width ratio of 1:4, and have an average spontaneous energy product of about 1X10 Gauss.Oersted. The width of the hexagonal sides of the platelets is less than 0.2 micron. The materials are compacted in a compression die to the shape of the contact at 450 C., while applying a pressure of 30,000 p.s.i. The magnetic fields of the platelets will be randomly oriented in this example.

EXAMPLE 6 The mechanical strength and the density of the composite system of example 5 can be increased by additional mechanical working as for example, forging, etc. In this example, a billet may be hot pressed according to the method disclosed in example 5. Then, the billet is hot forged to a dense structure and the contacts are machined out of it in a standard manner. These mechanical operations also diminish the size of the magnetic particles especially if they are brittle as is the situation in this example. By further mechanical working, barium hexaferrite particles of higher average spontaneous magnetic energy products is obtainable.

Various other kinds of mechanical operations will be discussed in other examples below.

EXAMPLE 7 Production of bodies of small dimensions by mechanical means and by using a temporary matrix is known in the art. For instance, William Hyde Wollaston (the English chemist) made very fine platinum wire by drawing it together with silver and subsequently the silver was selectively etched away. Also, US. Pat. Ser. No. 2,967,794 teaches the production of elongated particles of iron, nickel and cobalt by drawing them in a silver matrix and finally etching the silver selectively away. It appears that there has been no attempt made to date to produce contacts with additives of magnetic particles, diminishing the size of the magnetic particles by mechanical operations until they become spontaneous permanent magnets, and keeping the fine magnetic particles in the contact material matrix in order to achieve the superior magnetic contacts disclosed by this invention.

For example, 20 percent of a pulverized alloy containing about 30 percent iron and about 70 percent cobalt having an average particle size of 1 micron may be added to and thoroughly mixed with about 80 percent contact powder consisting of 90 percent silver and percent cadmium oxide. A billet is then pressed at 400 C. and 25,000 psi. After that, a number of rolling operations, followed by annealing opera tions at 600 C. are carried out. A diminishing ratio for the rolling operations is chosen so that the less ductile iron-cobalt alloy particles tear up and their size diminishes to the dimensions required to display sufficient spontaneous magnetization. The magnetic particles produced by this method are elongated in the same direction, The contacts may then be punched out, for example, from a final sheet having a suitable thickness.

EXAMPLE 8 It is known in the art that metal or alloy particles can be made much more brittle by certain additives which either precipitate at the crystal boundaries or form with the base alloy a more fragile alloy. As an example, addition of phosphorus to metals or alloys of the iron group will be here discussed. Iron-cobalt alloy particles are much more brittle if pure silver powder, for example, is treated in an auto-catalytic iron-cobalt plating bath (sometimes referred to as electroless plating). The thin iron-cobalt alloy deposits contain some phosphorus from a reducing hypophosphite agent which yields the brittleness. Less rolling operations are generally needed to reach the required size of the magnetic particles if this method is used.

EXAMPLE 9 About 20 percent Alnico V powder having an average particle size of 0.5 micron may be added to 80 percent contact material composed of about 88 percent silver and about 12 percent indium oxide. A hot-pressed billet is then subjected to subsequent rod-rolling and wire-drawing operations, with intermittent, annealing operations, at 500 C. The work is finished when the Alnico V powder is reduced to the size which is needed for the desired spontaneous magnetic energy. The diameter of the final rod or wire is planned to be that of the contact so that the contacts can be obtained by simple slicings.

EXAMPLE l0 A samarium-cobalt alloy may be produced by vacuum melting. Using a vacuum chamber, molten silver is held in a cruci ble at a temperature of l,000 C., the samarium-cobalt melt is allowed to drip into the molten silver in very small quantities which cool quite rapidly and form fine crystallites in the liquids silver. After a sufficient quantity of the samariumcobalt particles is produced in the silver melt, the melt is allowed to freeze into a billet while the Samarium-cobalt particles are kept in agitation (e.g., by vibration) in order to obtain a unifon-n distribution. Further treatment of the billet to refine the samarium-cobalt particles may be accomplished by various mechanical steps, such as, forging, rolling, drawing, etc. This technique can be used for various contact materials and magnetic alloys other than those specifically mentioned above. This example merely discloses one particular set of materials for purposes of illustration.

EXAMPLE 11 Some of the previous examples have disclosed methods for mechanical production which result in randomly or mechanically oriented magnetic particles which do not create optimum conditions. Complete magnetic alignment can be obtained only by the employment of magnetic-orienting fields. Such techniques are well known in the manufacturing of oriented pennanent magnets but have never been applied to the production of electrical contacts containing aligned spontaneously magnetized magnetic particles in a contact material matrix.

The simplest method involves the premixing of the contact and magnetic particles, as uniformly as possible. This premixing will prevent the sticking together of the magnetic particles when the magnetic-orienting field is applied. The filling of a compression die may then be carried out in the orienting magnetic field which aligns the particles in the desired direction and also aligns at the same time the magnetization vectors in a parallel manner. If subsequently a mechanical operation is employed to densify the composite system and/or to obtain further diminution of the size of the magnetic particles, care should be taken to choose the directions of the magnetic orientation and of the mechanical orientation during the working operations in such a way that they will be coincidental. lf this is done, all the magnetization vectors will remain parallel even after the mechanical reworking.

In the present example, about 10 percent bismuth manganide powder may be thoroughly mixed with about 70 percent tungsten carbide and about 20 percent silver powder. The strength of the aligning magnetic fieldis greater than 3,000 Oersted. The resulting powder is then hot pressed at 500 C. at a pressure of 15,000 psi. The resulting contacts will have a very long life and can be used, for example, as interruptors for automobile ignition circuits.

EXAMPLE 12 Magnetic metals and alloys can be oriented by amagnetic field during electrolytic, immersion or auto-catalytic deposition. In this example, silver-nickel alloy sheets of a thickness of 0.5 mil are electrolytically plated with an iron-cobalt alloy on one side and in a thickness of 0.5 micron while exposed to a uniform magnetic field. Over the iron-cobalt layer a 0.1 micron thick pure silver layer is plated. The silver-nickel alloy is used in this example as the basic contact material because this alloy resists any welding together of the contacts better than pure silver.

A great number of such sheets may be superimposed on one another and rolled together with great force. During rolling, the surfaces of pure silver weld together with the surfaces of silver-nickel sheets. lf the original magnetic orientation was perpendicular to the plane of the sheets, it will not change during the rolling operations. The rolling tears up the thinmagnetic sheets into small particles exhibiting an adequate percentage spontaneous magnetic energy. The rolled sheets are then cut into thin ribbons, in a direction perpendicular to the original positions of the silver-nickel sheets and contacts are subsequently punched out from the ribbons. The vector of the spontaneous magnetic field is in the plane of the contact and aligned in one direction. Any arc will thus be blown out perpendicularly to this vector and in the plane of the contact.

EXAMPLE [3 This example differs from the previous one only in that the magnetic alloy is deposited auto-catalytically for the purpose of making it more fragile and brittle.

EXAMPLE 14 Production of very fine iron or iron-cobalt alloy particles by electrodepositing iron or iron-cobalt in a mercury cathode has previously been known in the art. A percentage of these particles may exhibit spontaneous magnetization. Since mercury and the metals of the iron group do not alloy, the iron or ironcobalt particles are suspended in the mercury and they can be retrieved by vacuum distillation of the mercury. These particles can also be embedded into contacts. In this examples, the particles are immersed into an electroless silver immersion bath in which they are completely coated with a thin silver layer (e.g., 300 Angstroms thick). To these composite particles, fine pure silver particles are then mixed to obtain the desired ratio between magnetic and silver particles. Then contacts are made by utilizing the previously described compression, mechanical refining, etc., methods as desired.

EXAMPLE l5 The magnetic energy product of particles described in example 14 is especially high if the particles are produced while an orienting magnetic field-is applied during the electrode position into a mercury cathode. Elongated particles of highshape anisotropy can be obtained. Such particles can be effectively oriented by applying a magnetic field during compression and by maintaining this orientation during the subsequent mechanical operations, if any.

EXAMPLE 16 The thoroughness of mixing silver and magnetic particles can be greatly improved if the silver is first dissolved in mercury and the magnetic particles then deposited into an amalgam. Unfortunately, only about 0.06 percent silver can be dissolved in mercury while maintaining a binary system. Above the level a new phase (Ag Hg is generated and the amalgam freezes rapidly.

However, liquid cadmium amalgams with high-cadmium contents can be prepared. A percent cadmium containing amalgam is liquid 'above 40 C., and in an electrolytic bath operating, for example, at 80 C., 5 percent magnetic particles can be deposited in the amalgam. The cooled amalgam is kneaded over several times at room temperature, to obtain a uniform distribution. Then vacuum evaporation of the mercury is accomplished yielding a fine mixture of cadmium and magnetic (e.g., iron-cobalt) alloy particles. This mixture is then combined with silver powder having a ratio of about 85 percent silver, and 10 percent cadmium and about 5 percent iron-cobalt alloy particles. Contacts can then be made according to any of the above-discussed methods. The cadmium in the contacts has two main functions. First, during electrodeposition and evaporation, it prevents the undesirable growth of the magnetic particles. Secondly, it acts as an arc cooler in the contacts and helps to accelerate the extinguishing of the arc.

EXAMPLE 17 The blown out arc has to be sufficiently contained in a confined space in order to prevent an arcing over to another phase contact in the case where a two or more phase switch is utilized. This is usually accomplished by containing the arc within a shield. Such arc-containing shields are known in the art and generally consist of a heat resistant insulating material. A very desirable shield can be prepared using a mixture of heat resistant metals or alloys having a melting point above 400 C., with heat resistant inorganic compounds. In this example, a preferred shield may be made of a mixture of silver and a low-melting ceramic composition, the melting point of which is lower thari that of silver. A suitable alloy which may also be used for the shield is tungsten carbide. The ratio of the mixture is determined primarily by the desired resistivity. In this example, the resistivity lies between approximately 100 and 100,000 Ohm.cm. As FlG. 2 shows, the shield l surrounds the contacts 2 and 3, and is connected to the stationary contact 2 and thus is on the same electrical potential. When the moving contact 3 opens, the arc generated is blown out by the spontaneous magnetic particles in the contacts and the arc jumps from between the contacts 2 and 3 to between contact 3 and the shield l which is at the same electrical potential as contact 2. Due to the large resistance of the silver-ceramic mixture, the current is immediately reduced and the arc is extinguished. Shields such as that disclosed herein last much longer than previously used insulating shields.

In addition to arcs and sparksformed during the interruption and closure of the switch contacts, usually unwanted noise signals are created simultaneously. In circuits containing reactive components, switches during the closure and interruption operations may create large voltage or current transients which generate unwanted noises. One of the aims of this invention is to also smoothen the voltage and current profiles of the transients. This can be accomplished with switch contacts which contain at least two portions each larger than 0.030 inch in their three-dimensional diagonal. Also, each portion has a different specific resistivity. The minimum dimension of 0.030 inch serves to differentiate such contacts from those made of metal powder mixtures such as a mixture of silver and tungsten which may improve the refractory properties of the contact but have a finer texture than 0.030 inch.

EXAMPLE 18 In PK]. 3, a disc-type contact 4 is utilized which has a diameter of about 0.2 inch. The contact 4 has an inner disc 5 with a diameter of about 0.1 inch which consists of the mixture of about 80 percent silver, and about 20 percent magnetic particles displaying spontaneous magnetization of more than 0.5Xl0 Gauss.0ersted. The outer ring 6 of the contact is composed of a fine mixture of about 50 percent silver, about 30 percent magnesium oxide and about 20 percent of the mentioned magnetic particles. All the magnetic particles are oriented in such a way that the spontaneous magnetization vectors are parallel in one direction in the surface plane of the contact, as previously discussed.

Such a contact will interrupt the current in the following manner. The arc at the first moment of the interruption is generated in the center portion 5 of the contacts which is a very good conductor. The arc is then blown out perpendicularly to the direction of the magnetization vectors, in the surface plane of the contact. When the arc enters into the area of higher resistivity (outer ring 6) a resistance will be introduced into the circuitry which increases as the arc travels outwardly from the center portion 5 of the contact. When the resistance is too high to maintain an are, it will be extinguished. The resistance ranges between highand low-resistivity portions may vary greatly depending on the materials used. However, it has been found that excellent noise suppression can be obtained when the high-resistance portion 6 has a resistivity of about 5 to 5,000 times greater than the low-resistance portion 5. Also,

I it has been observed that the structure of F IG. 3 gives inexpec- EXAMPLE l9 The composition and structure of the contacts may be similar to that of example 18 except that neither the lownor the high-resistivity portions contain spontaneously magnetized particles. Instead, external magnets are provided for orienting magnetic field which blow the are from the low-resistivity portion of the contact to the high-resistivity portion.

EXAMPLE 20 The contact system of this example inserts a resistance both during the making and the breaking of the circuit. This method is primarily mechanical. While 'making contact, first the high-resistivity parts touch and at interruption the last disengaging parts are the high-resistivity portions of the contacts. There may be numerous methods for implementing this basic principle. FIG. 4 and 4A show one embodiment employing a parallelepipedon-shaped contact 7 having one low-resistivity portion 8 in the middle, and two high-resistivity portions 9 and 10 at the ends. As previously described above in example 18, the resistivities between highand low-resistivity portions may vary greatly but preferably are in the range of about 5 to 5,000: l. The contact 7 is preferably slightly bent as shown in FIG. 4. FIG. 5 depicts a working arrangement for such a pair of contacts. The moving contact 11 is attached to a spring member 12 which is pulled by a rod 13 which moves in bushing 14 to a position approximately parallel with the central axis of the stationary contact 15. When rod 13 is pulled to the left in the bushing 14, the spring shaft 12 of the moving contact 11 also moves to the left and parallel to itself because the joint between 12 and 13 is rigid. Contact 11 then touches the stationary contact 15 first at the point Ila-15a where the inserted resistance is maximum. Moving the shaft 13 further to the left, the springy element 12 begins to bend and the contact point between contacts 11 and 15 rolls downwards, toward the point llbl5 b thus causing the inserted resistance to decrease. FIG. 5A shows the position at which the contact areas llb-15b are in the middle of the contacts 11 and 15, respectively, and in which areas the inserted resistance is not more than the usual low value of a normal contact resistance. The contact areas 110 and 150 generally also have high resistance like areas 11a and 15a. Upon opening the contacts 11 and 15 the same events described above occur in the opposite sequence.

The principle for reducing noise suppression described in this example is capable of operating even without a magnetic field. For example, if the growing resistance between the two contacts, 11 and 15, changes with time according to a slope which insures that the inserted resistance is always smaller than the resistance which would allow the maintenance or the reignition of an arc, then any are will be steadily shorted out. On the other hand, if the growing inserted resistance does not short out an arc, it will be abruptly extinguished when the distance between the contacts is large enough but that would cause an unwanted noise effect. Even if for certain current values such conditions may prevail since the arc resistance depends on the amperage and larger currents might maintain such low-resistance arcs which would not be shorted out and extinguished gradually.

The operation shown in FIG. 5 minimizes the deleterious effects of bouncing. Contact bouncing may happen only while the high-resistivity portions of the contact are connected and that makes any spark erosion, welding probability, etc., negligible.

EXAMPLE 21 While the mechanical principle described above in example (FIGS. 5 and 5A) would possibly work with contacts having no magnetic arc control, especially at higher current values, it is possible that an arc could remain between the lowresistivity portions during interruption thus shorting out the inserted resistance. To avoid such possibilities a system having a stable permanent magnetic field in the direction of the plane of the contact surfaces is often desireable. This field may be supplied either by separate magnets or by spontaneously magnetized oriented magnetic particles distributed in the contacts. This example utilizes the presence of the two higher resistivity portions in the contact as described in examples l9 and 20, as well as a magnetic field. The are may be blown out in opposite directions, depending on the direction of the current. If the arc does not blow toward the moving contact parts, thus maintaining an arc free continuous interruption of the current, it will blow in a reverse manner and the interruption will still occur through an increasing resistance as described in detail in example 18.

When a magnetic field is present in the embodiment described in examples 20 and 21 the magnetic field may blow the arc toward portions Ila-15a, for example, in which case the growing inserted resistance is following the smooth change of the contact movement. If it is blown in the other direction, however, it will be extinguished in the area llc-ISc due to the large resistance there where the arc will gradually decrease in strength. This will occur before portions lla-IS a disengage, and thus a smooth gradual interruption may also be secured.

While various specific and preferred compositions, methods, structures and techniques have been described, the invention is not intended to be so limited since other suitable ways of accomplishing the results of the present invention will be apparent to those skilled in the art by virtue of this disclosure.

I claim:

1. An electrical switch contact having a contact material and embedded therein distinguishable magnetic particles, an adequate percentage of said magnetic particles having one single domain and with an average spontaneous magnetic energy product in excess of about 5,000 GaussOersted.

2. The electrical contact of claim 1 in which said magnetic particles are selected from the group consisting of ferromagnetic and ferrimagnetic particles.

3. The electrical contact of claim 2 in which the Curie temperature for said magnetic particles is in excess of 250 C.

4. The electrical contact of claim 2 in which more than one kind of magnetic particles is present.

5. The electrical contact of claim 2 in which said magnetic particles comprise from about 0.001 to 96 percent by weight of the total contact material.

6. The electrical contact of claim 2 in which said magnetic particles are aligned within said contacts so that they have fields which are oriented to provide a substantially unidirectional magnetic field in said contacts.

7. The electrical contact of claim 2 in which arc-cooling additives are present in said contacts.

8. An electrical switch having arc-extinguishing contacts comprising:

a. a first contact having embedded therein an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.0ersteds, said first contact being a stationary contact;

b. a second contact having embedded therein an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds, said second contact being a moveable contact; and

c. a high-resistance shield enclosing said first and second contacts with said shield being in electrical contact with said first contact to place said shield and said first contact at the same potential.

9. The electrical switch of claim 8 in which said shield comprises a mixture of metal or alloy having a melting point above 400 C., and a ceramic composition, the melting point of which is lower than that of said metal or alloy.

10. The electrical switch of claim 8 in which said shield has a resistivity in the range of about 100 to l00,000 ohm.cm.

11. The electrical switch of claim 8 in which said magnetic particles are selected from the group consisting of ferromagnetic and ferrimagnetic particles.

12. The electrical switch of claim 8 in which the Curie temperature for said magnetic particles is in excess of 250 C.

13. The electrical switch of claim 9 in which said shield metal is silver.

14. The electrical switch of claim 9 in which said shield alloy is tungsten carbide.

15. The electrical switch of claim 11 in which said magnetic particles comprise from about 0.001 to 96 percent by weight of the total contact material.

16. The electrical switch of claim 11 in which said magnetic particles are aligned within said contacts so that they have fields which are oriented to provide a substantially unidirectional magnetic field in said contacts.

17: The electrical switch of claim 11 in which more than one kind of magnetic particles is present.

18. The electrical switch of claim 11 in which arc-cooling additives are present in said contacts.

19. An electrical switch contacts comprising magnetic particles embedded in said contacts, said magnetic particles having an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.0ersteds, said contacts having at least two portions, each of said portions having a three dimensional diagonal in excess of about 0.30 inch and each portion having different specific resistivities.

20. An electrical switch contact comprising:

a. an inner portion in which are embedded first magnetic particles having an adequate percentage of single domain particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds; and,

b. an outer portion adjacent said inner portion having embedded therein second magnetic particles having an adequate percentage of single domain particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.0erteds, said outer ring portion having a resistivity higher than the resistivity of said inner disc. The electrical contact of claim 20 in which said first and second magnetic particles have spontaneous magnetization vectors which are oriented so that they are parallel in one direction in a surface plane of said contacts.

21. The electrical contact of claim 20 in which said first and second magnetic particles have spontaneous magnetization vectors which are oriented so that they are parallel in one direction in a surface plane of said contacts.

22. The electrical cpntact of claim 21 in which said inner portion is disc shaped and said outer portion is ring shaped.

23. The electrical contact of claim 21 to which said contact is in the shape of a parallelepipedon having at least three sections: a first section being centrally located and constituting said inner portion of said contact; and second and third sections adjacent to said first section and on opposite sides thereof, said second and third sections constituting said outer portion of said contact.

l i l i I. 

1. An electrical switch contact having a contact material and embedded therein distinguishable magnetic particles, an adequate percentage of said magnetic particles having one siNgle domain and with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersted.
 2. The electrical contact of claim 1 in which said magnetic particles are selected from the group consisting of ferromagnetic and ferrimagnetic particles.
 3. The electrical contact of claim 2 in which the Curie temperature for said magnetic particles is in excess of 250* C.
 4. The electrical contact of claim 2 in which more than one kind of magnetic particles is present.
 5. The electrical contact of claim 2 in which said magnetic particles comprise from about 0.001 to 96 percent by weight of the total contact material.
 6. The electrical contact of claim 2 in which said magnetic particles are aligned within said contacts so that they have fields which are oriented to provide a substantially unidirectional magnetic field in said contacts.
 7. The electrical contact of claim 2 in which arc-cooling additives are present in said contacts.
 8. An electrical switch having arc-extinguishing contacts comprising: a. a first contact having embedded therein an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds, said first contact being a stationary contact; b. a second contact having embedded therein an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds, said second contact being a moveable contact; and c. a high-resistance shield enclosing said first and second contacts with said shield being in electrical contact with said first contact to place said shield and said first contact at the same potential.
 9. The electrical switch of claim 8 in which said shield comprises a mixture of metal or alloy having a melting point above 400* C., and a ceramic composition, the melting point of which is lower than that of said metal or alloy.
 10. The electrical switch of claim 8 in which said shield has a resistivity in the range of about 100 to 100,000 ohm.cm.
 11. The electrical switch of claim 8 in which said magnetic particles are selected from the group consisting of ferromagnetic and ferrimagnetic particles.
 12. The electrical switch of claim 8 in which the Curie temperature for said magnetic particles is in excess of 250* C.
 13. The electrical switch of claim 9 in which said shield metal is silver.
 14. The electrical switch of claim 9 in which said shield alloy is tungsten carbide.
 15. The electrical switch of claim 11 in which said magnetic particles comprise from about 0.001 to 96 percent by weight of the total contact material.
 16. The electrical switch of claim 11 in which said magnetic particles are aligned within said contacts so that they have fields which are oriented to provide a substantially unidirectional magnetic field in said contacts.
 17. The electrical switch of claim 11 in which more than one kind of magnetic particles is present.
 18. The electrical switch of claim 11 in which arc-cooling additives are present in said contacts.
 19. An electrical switch contacts comprising magnetic particles embedded in said contacts, said magnetic particles having an adequate percentage of distinguishable single domain magnetic particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds, said contacts having at least two portions, each of said portions having a three dimensional diagonal in excess of about 0.30 inch and each portion having different specific resistivities.
 20. An electrical switch contact comprising: a. an inner portion in which are embedded first magnetic particles having an adequate percentage of single domain particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oersteds; and, b. an outer portion adjacent said inner portion having embedded therein second magnetic particles having an adequate percentage of single domain particles with an average spontaneous magnetic energy product in excess of about 5,000 Gauss.Oerteds, said outer ring portion having a resistivity higher than the resistivity of said inner disc. The electrical contact of claim 20 in which said first and second magnetic particles have spontaneous magnetization vectors which are oriented so that they are parallel in one direction in a surface plane of said contacts.
 21. The electrical contact of claim 20 in which said first and second magnetic particles have spontaneous magnetization vectors which are oriented so that they are parallel in one direction in a surface plane of said contacts.
 22. The electrical contact of claim 21 in which said inner portion is disc shaped and said outer portion is ring shaped.
 23. The electrical contact of claim 21 to which said contact is in the shape of a parallelepipedon having at least three sections: a first section being centrally located and constituting said inner portion of said contact; and second and third sections adjacent to said first section and on opposite sides thereof, said second and third sections constituting said outer portion of said contact. 